As a semiconductor wafer used now, for example, there are a silicon wafer, an epitaxial (EP) wafer, a wafer of Silicon on Insulator (SOI), and so forth. Semiconductor devices are produced by forming devices on these wafers. In recent years, a semiconductor device has been required to be finer, to be higher integrated, to have a higher speed, to have a higher yield, and so on. It has been said that among them, performance or yield of a formed semiconductor wafer reflects quality of the wafer.
For example, quality of a thermal oxide film formed by thermally oxidizing the semiconductor wafer is one of particularly important qualities in the semiconductor wafer, and reflects goodness or badness of the condition of forming the oxide film, crystal quality in a surface of the semiconductor wafer, and so forth. Moreover, an electric characteristic of a Metal Insulator Semiconductor (MIS) capacitor reflects quality of an insulator film formed on the semiconductor wafer, and particularly reflects crystal quality in a surface of the semiconductor wafer and in the vicinity of the surface, as well as the quality itself of the insulator film. It has been more important from now to provide semiconductor wafers of high quality by making it possible to higher-sensitively and higher-precisely evaluate an electric characteristic of the insulator film formed on the semiconductor wafer.
However, in the case of forming a MIS capacitor for evaluating a semiconductor wafer, a process of forming the MIS capacitor requires a large-scale apparatus and multiple steps and there had been troubles such as large burden to cost and lack of rapidity.
Accordingly, methods for evaluating a semiconductor wafer by using an electrode made of mercury being excellent in convenience have been developed. And, there have been proposed C-V method of measuring an interface state in the interface between the semiconductor wafer and the oxide film, a dopant density of the bulk in the semiconductor wafer, or the like, and Pseudo MOS FET method for evaluating an SOI wafer (see, for example, Japanese Patent Application Laid-open (kokai) No. 2001-60676, Japanese Patent Application Laid-open (kokai) No. 2001-267384, and S. Cristoloveanu et al., “A Review of the Pseudo-MOS Transistor in SOI Wafers: Operation, Parameter Extraction, and Applications” IEEE Trans. Electron Dev, 47, 1018 (2000), H. J. Hovel, “Si film electrical characterization in SOI substrates by HgFET technique”, Solid-State Electronics, 47, 1311 (2003)).
However, in such evaluation methods, the contact state between the semiconductor wafer and the electrode is very important for obtaining a C-V characteristic or a FET characteristic.
For example, in Japanese Patent Application Laid-open (kokai) No. 2001-60676 or Japanese Patent Application Laid-open (kokai) No. 2001-267384, a method of spearing and contacting a needle-shaped probe as the electrode has been disclosed. However, there is a problem that in the case of a needle-shaped probe, the tip end of the needle is distorted or friction scrap of the object to be measured adheres thereto, and thereby contact resistance becomes larger.
On the other hand, in S. Cristoloveanu et al., “A Review of the Pseudo-MOS Transistor in SOI Wafers: Operation, Parameter Extraction, and Applications” IEEE Trans. Electron Dev, 47, 1018 (2000), or in H. J. Hovel, “Si film electrical characterization in SOI substrates by HgFET technique”, Solid-State Electronics, 47, 1311 (2003), a mercury probe is used as the electrode. In such mercury to be used as an electrode, foreign matter such as dust is occasionally mixed in evaluating a semiconductor wafer. The mercury electrode is directly in contact with the semiconductor wafer and an electric characteristic thereof is measured. Therefore, the mercury electrode is very sensitive to contamination in the mercury. If foreign matter such as dust is mixed in the mercury, the foreign matter causes change of the contact area between the wafer and the mercury electrode, and serves as a leak source or an insulator, depending on a type of the impurities. Therefore, occasionally, the electric conductivity has become unstable and abnormality has been shown in the measured electric characteristic.
In order to solve the problem in the semiconductor wafer evaluation due to such mixing of foreign matter to the mercury, for example, in Japanese Patent Application Laid-open (kokai) No. H06-140478, there has been disclosed a contact type inspection apparatus in which pressures in a pressure chamber for adjusting a height of a probe head and in a pressure chamber for thrusting mercury are certainly held to predetermined set values and by which labor of an operation for setting pressure and an operation for adjusting the pressure can be reduced and high precision inspection can be performed.